Typically, when a TFT LCD panel (TFT LCD panel is an LCD panel used in an in active matrix array) is driven, it is necessary to apply voltages with different polarities to the liquid crystal used in the LCD at predetermined durations because it may be damaged if voltage with the same polarity is continuously applied. For example, this is not a problem if a driver circuit driving the LCD panel can output signals in a range from +5V to -5V. However, the problem occurs in a case where the TFT LCD panel is driven by using a source driver which can output only up to 5V in one polarity. In such a case, the above-mentioned alternating current driving has been apparently performed by swinging the driving voltage for common electrode in a range between 0V and about 5V (sometimes, -1V and +6V). The common electrode is a capacitive load which requires relatively high power of as much as 0.5 W for charge and discharge for VGA (640.times.480 pixels).
FIGS. 4 and 5 show an example of the background art. FIG. 4 shows a TFT LCD panel 100. The LCD panel 100 comprises a column driver 200 for distributing a video signal to each source line 102, a row driver 300 driving each gate line 104, transistors 106 the source of which is connected to the source line 102, the gate of which is connected to the gate line 104, and which exist in the number of pixels, liquid crystal (illustrated as capacitors 108), and a common electrode 12 mounted on a surface opposite to the transistors 106. Because this TFT LCD panel 100 is of a conventional type, further description is not given. When the column driver 200 outputs a signal on the source line 102, a transistor 106, which is connected to a gate line turned on by the row driver 300, drives the liquid crystal 108 with the voltage output on the source line 102 so as to display a desired image.
Here, if the column driver 200 driving the source line can output a signal only 5V in one polarity as mentioned earlier, the voltage for the common electrode 12 must be swung between 0V and about 5V. Since the circuit at and after the liquid crystal 108 as viewed from the common electrode 12 is a capacitive load as described earlier, it appears to be a capacitance C.sub.P (about 0.2 .mu.F) as shown in FIG. 5. This capacitance has been driven by a driver 400.
Such drive method for the common electrode 12 needs much power. When such LCD panel is used for a notebook computer, power saving is one of major problems. Reducing power consumed by the LCD panel leads to extension of available time of the entire computer.
Another example of the background art is found in PUPA 5-265406 which discloses a device in which containing multiple electrodes, one common electrode is short circuited to another one in common inversion to transfer charges stored in one common electrode to the other, and, then, a driver circuit drives it to desired potential. However, this approach requires a special common electrode. In addition, short-circuiting only makes the potential in two common electrodes equivalent, and driving by the drive circuit is required for making the common electrode the desired voltage so that reduction of power consumption would be small.